C++ loop error that my professor can't figure out - c++

Question

I am currently taking a C++ programming class and am working on a project in which I have to create a fairly simple movie database. My code essentially works as intended yet in certain cases it causes the main menu to loop infinitely and I cannot figure out why. I brought this to my teacher and he cannot explain it either. He gave me a workaround but I would like to know if anyone can see the cause of the problem. Full code is as follows:
#include <cstdlib>
#include <iostream>
#include <vector>
#include <string>
using namespace std;
struct MovieType
{
string title;
string director;
int year;
int length;
string rating;
};
MovieType addMovie() {
MovieType newMovie;
cout << "Movie title :";
getline(cin, newMovie.title);
cout << "Director :";
getline(cin, newMovie.director);
cout << "Year :";
cin >> newMovie.year;
cout << "Length(in minutes) :";
cin >> newMovie.length;
cout << "Rating :";
cin >> newMovie.rating;
cout << endl;
return newMovie;
}
void listMovie(MovieType movie) {
cout << "______________________________________" << endl;
cout << "Title : " << movie.title << endl;
cout << "Director : " << movie.director << endl;
cout << "Released : " << movie.year << endl;
cout << "MPAA Rating : " << movie.rating << endl;
cout << "Running time : " << movie.length << " minutes" << endl;
cout << "______________________________________" << endl;
}
void search(vector<MovieType> movieVector) {
string strSearch;
cout << endl << "Search title: ";
getline(cin, strSearch);
for (int c = 0; c < movieVector.size(); c++) {
if (movieVector.at(c).title == strSearch)
listMovie(movieVector.at(c));
}
}
int main() {
bool quit = 0;
vector<MovieType> movieVector;
while (quit == 0) {
char selection = 'f';
cout << "Main Menu:" << endl;
cout << "'a' - Add movie" << endl;
cout << "'l' - List movies" << endl;
cout << "'s' - Search by movie title" << endl;
cout << "'q' - Quit" << endl;
cout << "Please enter one of the listed commands:";
cin >> selection;
cin.ignore();
cout << endl;
if (selection == 'a')
movieVector.push_back(addMovie());
else if (selection == 'l') {
for (int c = 0; c < movieVector.size(); c++) {
listMovie(movieVector.at(c));
}
}
else if (selection == 's') {
search(movieVector);
}
else if (selection == 'q')
quit = 1;
}
return 0;
}
When an unexpected input type is entered during the addMovie function(like entering text for the int type year), it just runs through the function then loops through the menu infinitely. It appears to me that the code just stops even looking at the input stream. I have tried using cin.ignore() in many different places but it doesn't matter if there is nothing left in the stream it just keeps going.
I am using NetBeans to compile my code.
I really have no idea why it behaves like this otherwise I would offer more information but I am just curious as to why this happens, because as I said before, my professor doesn't even know why this is happening.
Any help or insight is greatly appreciated.

Answer 1

cin enters an error state where cin.fail() is true. In this state it just ignores all input operations. One fix is to clear the error state, but better, only use getline operations on cin, not formatted input.
E.g., instead of
cin >> newMovie.year;
… do
newMovie.year = stoi( line_from( cin ) );
… where line_from can be defined as
auto line_from( std::istream& stream )
-> std::string
{
std::string result;
if( not getline( stream, result ) )
{
// Throw an exception or call exit(EXIT_FAILURE).0
}
return result;
}
Disclaimer: code untouched by compiler.